V70 towing question 1967 Airstream Caravel
 

I posted on another forum this question.. traveling from Ok City to my home in SC, mpg started around 13 and ended up at 21. It happened gradually. I suspect that my Volvo V70 CPU took over 1000 miles to calibrate a fuel mixture that reaped this phenomenal result. I hoped to find a way to speed up the process. Before I go on.. you should know that I am sure of these figures and I am not a liar.. which many believe I am on the other forum. Both the MPG meter and my math confirmed this. My math abilities are quite advanced.. being a retired mechanical engineer.

Has anyone else done so well with MPG? and can anyone here answer my question? I will bring this question to the Airstream people too.

car is a 05 Volvo V70 with a non turbo 2.4 5 cylinder engine. Car has 150,000 miles, it drives like new and gets 31 on the hwy not towing. Caravel is complete and weighs around 2500 lbs.